Method for preparing metallurgical-grade alumina by using fluidized bed fly ash

Abstract

Provided a method for preparing metallurgical-grade alumina by using fluidized-bed fly ash, comprising: a) removing iron by wet magnetic separation after crushing the fly ash; b) reacting the fly ash after magnetic separation with hydrochloric acid to obtain a hydrochloric leachate; c) passing the hydrochloric leachate through macro-porous cationic resin to deeply remove iron to obtain a refined aluminum chloride solution; d) concentrating and crystallizing the refined aluminum chloride solution to obtain an aluminum chloride crystal; and e) calcining the aluminum chloride crystal to obtain the metallurgical-grade alumina. The method is simple, the procedure is easy to be controlled, the extraction efficiency of alumina is high, the production coast is low, and the product quality is steady.

Description

[0001]This application is a national phase of International Application No. PCT / CN2011 / 073371 filed Apr. 27, 2011 and claims priority to Chinese Application No. 201010161879.X filed Apr. 27, 2010.TECHNICAL FIELD[0002]The present invention relates to a comprehensive utilization of fluidized-bed fly ash and in particular relates to a method for preparing metallurgical-grade alumina by using the fluidized-bed fly ash.BACKGROUND[0003]Fly ash is a waste discharged from the coal-fired power station. In China, the coal is used as one of the main energy sources and hundreds of millions tons of fly ash are discharged from power stations each year. The discharge of the fly ash not only occupies a large area of land, but also pollutes the environment seriously. How to handle and utilize the fly ash becomes a very important problem. The fly ash contains a number of components that can be utilized, for example, circulating fluidized-bed fly ash usually contains about 30 to 50 percent by weight o...

AI Technical Summary

Benefits of technology

[0010]The object of the invention is to provide an improved method for preparing metallurgical-grade alumina by using the fly ash as the raw material. The method is simple, the production cost is low, and the product quality is steady.

[0043]As compared with the processes in the prior art, the advantages of the present invention are as the following aspects. The method is simple, the procedure is easy to be controlled, the extraction efficiency of alumina is high, the production coast is low, and the product quality is steady. The circulating fluidized-bed fly ash with high activity is adopted as the raw material for the invention and alumina is extracted from the fly ash via direct acid-leaching process, which saves the step of calcination with presence of sodium carbonate at a high temperature and thus simplifies the procedures and reduces the production cost. Moreover, without addition of alkali, sodium oxide as an impurity can be avoided being introduced in the system. The acid leaching of the fly ash occurs in acid-resisting reactor at a moderate temperature (in the range of 100-200° C.), and thus the leaching efficiency of alumina is high, being 80% or more. As compared with de-ironing process via alkali leaching method, the de-ironing process via the combination of magnetic separation and the resin adsorption is simpler, the production cost is lower, and iron removing effect is better. The alumina product obtained via the method according to the invention contains Al2O3 of 98.9 wt % or more, Fe2O3 of 0.004 wt % or less, SiO2 of 0.02 wt % or less and Na2O of 0.008 wt % or less, which meets the requirements on purity of metallurgical-grade alumina Class I described in Nonferrous Metal Industry Standard “YS / T274-1998 Alumina” of the People's Republic of China. In particular, the contents of Fe2O3 and Na2O in the product of the invention are much less than the Standard values of 0.02 wt % and 0.5 wt % respectively. As compared with the major alumina-producing enterprises (such as Alcoa of Australia Ltd., Spanish Alumina Ltd., Queensland Alumina Ltd., Aluminum de Greece, Kaiser Aluminum Corp.), the alumina product obtained via the method of the present invention is better than other similar products in Al2O3 content and impurities (such as Fe2O3, SiO2 and Fe2O3) contents.

[0044]In addition, since the improved magnetic separation apparatus is used in the present invention, the iron removing efficiency is improved by 20% or more, and the iron removing rate is improved from 60% to 80%, which significantly relieving the burden of de-ironing from solution in the subsequent processes, and thereby reducing the production cost and improving the production efficiency.

Problems solved by technology

The discharge of the fly ash not only occupies a large area of land, but also pollutes the environment seriously.

How to handle and utilize the fly ash becomes a very important problem.

However, there are many disadvantages exist in this process.

Firstly, large quantities of silicium-calcium slag is produced during the leaching process.

Such silicium-calcium slag is prone to be another discharge of waste which even requires more occupancies if the slag can not be consumed thoroughly by the building materials market.

Further, the silicone dioxide is not utilized with a high value.

Secondly, the energy consumption in the limestone sintering process is very high, since the fly ash is calcined in a very high temperature, and the requirements on its procedures and equipments are also high.

Thirdly, the recovery efficiency of alkali is very low as large quantities of slag are produced during the alkali leaching process, which increases the production cost.

However, the energy consumption of the process is high and its procedures are complicated since the fly ash needs to be calcined in a very high temperature and the calcined ash needs to further act with acid in order to separate silicone and aluminum.

The fly ash usually reacts with acid at a temperature lower than 300° C. As compared with the high calcination temperatures used for the limestone sintering method and sodium carbonate sintering method, the energy consumption of the acid leaching method decreases dramatically.

Furthermore, some impurities, such as calcium and sodium, will not be introduced in the alumina product.

However, one of the defects of the acid leaching method resides in that soluble impurities, such as iron, will enter the solution, resulting in that the obtained alumina contains quite a number of iron and the like which are difficult to be removed.

Since acid dissolving and alkali dissolving are both necessary in such method, its processes are complicated and its production cost is increased.

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